1. Field of the Invention
This invention is related to lubricants, especially lubricating oils, and, more particularly, to a class of ashless and non-phosphorus-containing anti-wear additives derived from alcohols that are the reaction products of mercaptobenzothiazoles, mercaptothiazolines, or mercaptobenzimidazoles with various epoxides.
2. Description of Related Art
In developing lubricating oils, there have been many attempts to provide additives that impart antifatigue, antiwear, and extreme pressure properties thereto. Zinc dialkyldithiophosphates (ZDDP) have been used in formulated oils as antiwear additives for more than 50 years. However, zinc dialkyldithiophosphates give rise to ash, which contributes to particulate matter in automotive exhaust emissions, and regulatory agencies are seeking to reduce emissions of zinc into the environment. In addition, phosphorus, also a component of ZDDP, is suspected of limiting the service life of the catalytic converters that are used on cars to reduce pollution. It is important to limit the particulate matter and pollution formed during engine use for toxicological and environmental reasons, but it is also important to maintain undiminished the antiwear properties of the lubricating oil.
In view of the aforementioned shortcomings of the known zinc and phosphorus-containing additives, efforts have been made to provide lubricating oil additives that contain neither zinc nor phosphorus or, at least, contain them in substantially reduced amounts.
Illustrative of non-zinc, i.e., ashless, non-phosphorus-containing lubricating oil additives are the reaction products of 2,5-dimercapto-1,3,4-thiadiazoles and unsaturated mono-, di-, and tri-glycerides disclosed in U.S. Pat. No. 5,512,190 and the dialkyl dithiocarbamate-derived organic ethers of U.S. Pat. No. 5,514,189.
U.S. Pat. No. 5,512,190 discloses an additive that provides antiwear properties to a lubricating oil. The additive is the reaction product of 2,5-dimercapto-1,3,4-thiadiazole and a mixture of unsaturated mono-, di-, and triglycerides. Also disclosed is a lubricating oil additive with antiwear properties produced by reacting a mixture of unsaturated mono-, di-, and triglycerides with diethanolamine to provide an intermediate reaction product and reacting the intermediate reaction product with 2,5-dimercapto-1,3,4 thiadiazole.
U.S. Pat. No. 5,514,189 discloses that dialkyl dithiocarbamate-derived organic ethers have been found to be effective antiwear/antioxidant additives for lubricants and fuels.
U.S. Pat. Nos. 5,084,195 and 5,300,243 disclose N-acyl-thiourethane thioureas as antiwear additives specified for lubricants or hydraulic fluids.
The reaction of mercaptobenzothiazole (MBT) with epoxides is taught in the family of patents by Camenzind et. al. (EP 0 894 793; U.S. Pat. Nos. 6,100,406; 6,255,259). Example 1 in U.S. Pat. No. 6,255,259 teaches reacting MBT with propylene oxide. However, the resulting intermediate is not recognized by Camenzind as having utility as a lubricant additive in its own right. Rather, it is reacted further with a phenolic antioxidant compound to form a mixed phenolic/MBT additive. The same can be said for Example 12, where glycidal neodecanoate (Glydexx® N-10) is reacted with MBT, but the product again is reacted further with a phenolic antioxidant derivative. The intermediates are not shown to have been tested for anti-wear performance.
This multi-step process is disadvantageous, as the additional reaction steps must result in higher processing costs and added undesirable waste.
Zhang et al (Wear, 1999, 224(1), 50-55) evaluated a dithiocarbamate as a lubricant additive where a glycidaldithiocarbamate is linked to a benzothiazoylthio moiety.
Zhang et al. improved the solubility of MBT in oil by introducing the dialkyl dithiocarbamate group. The dithiocarbamate group has long been known to have anti-wear and extreme pressure activity. However, dithiocarbamates can also be undesirable, as they are corrosive towards copper, and attack engine seals. Furthermore, the dithiocarbamate group contributes additional sulfur content to the additive. This is not desirable in light of recent trends towards lower sulfur lubricants, which are in turn being driven by government requirements for lower sulfur fuels.
Neither Camenzind nor Zhang discloses or suggests that reacting mercaptobenzothiazole with an epoxide that does not contain an additional functional group that is known to possess utility as a lubricant additive will result in an additive with superior anti-wear performance.
U.S. Pat. No. 6,187,726 discloses compounds and lubricant compositions that comprise a substituted linear thiourea of the structure
wherein R1, R2, and R4 are independently selected from the group consisting of alkyl, alkenyl, aryl, alkaryl, aralkyl, and hydrogen; R3 is selected from the group consisting of alkyl, alkenyl, and combinations thereof; X is selected from the group consisting of (i) methylene, if, and only if, R3 is alkylene, (ii) oxygen, and (iii) sulfur; and A is selected from the group consisting of alkylene and aryl.
U.S. Pat. No. 6,551,966 discloses a composition comprising:
(A) a lubricant, and
(B) at least one 5-alkyl-2-mercapto-1,3,4-oxadiazole compound of the formula:
wherein R1 is a hydrocarbon or functionalized hydrocarbon of from 1 to 30 carbon atoms.
U.S. Pat. No. 6,559,107 discloses a composition comprising:
(A) a lubricant, and
(B) at least one 5-alkyl-2-thione-1,3,4-thiadiazolidine compound of the formula:
wherein R1 is a hydrocarbon or functionalized hydrocarbon of from 1 to 30 carbon atoms, R2 and R3 are independently selected from the group consisting of hydrocarbon or functionalized hydrocarbons of from 1 to 30 carbon atoms and hydrogen, and X is oxygen, sulfur or nitrogen.
U.S. Pat. No. 6,566,311 discloses a composition comprising: (A) a lubricant, and (B) at least one 1,3,4-oxadiazole compound of the formula:
wherein R1 is selected from the group consisting of hydrogen, linear or branched alkyl, alkenyl, alkaryl, aryl, alkyl ether, and alkyl ester; R2, R3, and R4 are independently selected from the group consisting of hydrogen, linear or branched alkyl, alkenyl, alkaryl, and aryl; and any alkyl moiety can optionally contain within it oxygen ether, ester, or amide groups.
The disclosures of the foregoing references are incorporated herein by reference in their entirety.